This invention relates to a process and an apparatus for producing melt spun multi-layered cross section multi-component filaments. These filaments can be collected and processed into nonwoven webs for use in filters, apparel, wipes, and hygiene products.
In a melt spinning process, thermoplastic synthetic polymers are melted and forced through orifices of a spinneret to form filaments. These filaments can be drawn or attenuated via air jets or mechanical means and collected on a moving porous surface to produce a random laydown of filaments or nonwoven web. The web can be bonded together to maintain its integrity. Also, in a melt blowing process, air jets can be added at the end of the spinneret to provide a very rapid drawing process providing very small diameter filaments.
In order to produce uniform filaments from a row of spinneret orifices, the polymer of each filament should be subjected to as nearly as possible the same heat history and residence time in the spinning apparatus. This can be accomplished using a polymer distribution manifold, which makes molten polymer with a longer travel distance move more quickly than molten polymer with a shorter travel distance. An example of a distribution manifold is a coat hanger (indicative of the general shape of the manifold) which can be found in U.S. Pat. Nos. 3,860,383; 4,043,739; 4,285,655; 5,728,407; and 6,120,276.
Bicomponent filaments which are made from two different polymers can also be melt spun. The separate molten polymer flow streams can be combined into layered polymer flow streams to make filaments with side-by-side cross sections in which filament portions each have distinct polymer components that extend for a significant portion of the length of each filament. An example of this in a meltblown process is U.S. Pat. No. 6,057,256. It is known, when making side-by-side cross section filaments, to combine polymer flow streams prior to using a coat hanger. Unfortunately, this eliminates the capacity for downstream filtering as filtering of the bicomponent melt stream would cause mixing of the layered polymer streams. It is also known, to use a coat hanger for each polymer flow stream and then to feed the polymer flow streams to a split hole die before being combined. Unfortunately, this split hole die can produce non-uniform filaments.
In systems where the polymers are not filtered, there are a significant number of spinneret orifices that plug during the start-up of the die and during operation, as the orifices are not protected from particles that come through the melt system. Essentially all melt processes will form particles that are large enough to plug the spin orifice. The source of these particles can be degraded polymer, gels, agglomerates, contaminants, etc. For most processes the typical number of plugged holes will start at 10-15% and will continue to increase during the run.
In the prior art processes, when the polymers are combined before the melts exit the die, an interface exists between the two polymer melts. This interface is not directly controlled and can be influenced by many factors in the process. Two examples of the significant problems that can occur due to the lack of control of this interface are 1) when using two similar polymers the interface may start to diffuse as the polymers start to mix and thus the fiber will be more a melt blend fiber versus a bicomponent fiber; and 2) if the polymers have a significant difference in melt viscosity, it is possible the higher viscosity polymer will start to fill a disproportionate amount of the space available to the melt which will likely result in a mismatch in the speed of the two melts as they are exiting the die, as the polymer melts can slide past each other along the interface which will likely cause spinning problems. There is a need for a melt spinning apparatus and process for making uniform multi-layered cross section filaments which allow for downstream filtering, the use of polymers with different melt viscosities, and minimizing the contact time for undesirable mixing between molten polymers.
In a first embodiment, the present invention is directed to a process for preparing a plurality of multi-layered filaments from multiple thermoplastic synthetic polymers comprising separately melting and extruding multiple thermoplastic synthetic polymers into separate molten polymer flow streams, distributing said separate molten polymer flow streams into separate planar molten polymer flow streams, then filtering said separate planar molten polymer flow streams, and feeding said separate planar molten polymer flow streams into a spinneret comprising a plurality of separate polymer flow passages, wherein each planar molten polymer flow stream is fed to a separate series of said polymer flow passages communicating with spinneret exit orifices, which are aligned such that multiple molten polymer flow streams emerging from said exit orifices are directed into contact with one another to form multi-layered filaments.
Another embodiment of the present invention is an apparatus for carrying out the process described above, comprising multiple extruders for separately melting and extruding multiple thermoplastic synthetic polymers into molten polymer flow streams, separate distribution manifolds downstream of and communicating with said extruders for distributing said separate molten polymer flow streams into separate planar molten polymer flow streams, separate filters downstream of and communicating with said distribution manifolds for filtering said separate planar molten polymer flow streams, and a spinneret, downstream of and communicating with said filters, comprising a plurality of separate polymer flow passages for transporting each of said separate planar molten polymer flow streams to a plurality of spinneret exit orifices, said passages being aligned such that separate molten polymer flow streams emerging from the exit orifices come into contact with one another to form multi-layered filaments.
A further embodiment of the present invention is directed to a melt spinning beam for use in the process and apparatus described above which comprises multiple polymer inlet passages each communicating with separate multiple coat hanger distribution manifolds, separate filters downstream of and communicating with each coat hanger distribution manifold, and a spinneret downstream of and communicating with said filters, said spinneret having a plurality of separate polymer flow passages communicating with exit orifices for spinning of said multi-layered filaments.